Horizontal magnetic deflection system for television receivers



OC- 8,1957' P G woLFE 2,809,327

HORIZONTAL MANE'TIc DEFLECTION SYSTEM FOR TELEVISION REcEIvERs Filed Nov. 17, 1955 H/GH VOLT/76E FR Cl? 72/55 PHI/L q. wm FE l? TTORNEY United StatesY Patent O HORIZNTAL MAGNETIC DEFLECTIN SYSTEM FOR TELEVISION RECEIVlERSY Paul G. Wolfe, Oreland, Pa., assignorto Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application November 17,1955, Serial No. 547,407 9 Claims. Y (Cl. 315.-27)

This invention relates to horizontal magnetic dellection systemsV in television receivers, and more particularly the invention relates tothe elimination or. minimization of ringing currents in the horizontal deflection coils of the deflection system.

The horizontal magnetic deflection system now commonly employed in' television receivers includes an output yor driver tube, an output transformer, a. magnetic deflection yoke whose horizon-tal deflectionicoils `are connected to the transformer, and adamper tubeyoperatively `associated with the horizontal deflection coils. Usually, the transformer is an autotransformer, and high voltage for the secondanodeyofthe cathode ray tube is derived lation, and by providing a switching diode in one of theV effectively insert and remove one therefrom. A signal of suitable form. is supplied to" the driver tube which conducts `during approximately the whole of the trace interval and is cut olf during the retrace interval. Upon cut off of` the` driver tube, the energy in the yoke isclissipated by transferring the energy by means of `the autotransformerto highvoltage power.

A-s is wellknown, the mode of operation and the oscillatorycharacterfof the deliection system cause undesired transient-oscillations, givingriseto4 so-calledV ringing cur- :rentswhich'tend-to-persist through the trace interval and tend to`produce; noticeable-visual effects inA the image. Furthermore, while-it isf economically advantageous to derive high voltage from the deflection system for application to the-second auode of theV cath-ode ray tube, -inV such" aiisyste'mthe ringingV- currents are more pronounced and more troublesome.` l

Numerous proposalshave -been made in the past' for thel elimination-or minimization of' these undesired currents and their effects, but none of them has been adequate in practice to provide awholly satisfactoryv solution ofthe problem.` i

Accordingly, one object of? the'present invention is. to provide a satisfactorysolution of this problem.

lAnother'object of theinventionis to provide a simple andhighly effective arrangement for lsubstantially eX- cluding ringing currents from the horizontal' ydeflection coils;

Still another obje'ctof the inventionis to provide an arrangement wherein substantial exclusion of the ringing currents from the horizontal deflection coils is accomplished by electively'isolating the source of ringing currents from thedeflecti'ng coils. A

'ln prior attempts to solve the problemof ringing currents, the Iapproach generally has` been toward the provision of means to-dissipate or damp :such currents or divertthem away from, the deiecting coils.

The `present invention is based upon a new and differentV approach tothe problem. It Awas first determined thatthe ringing currents originate in the transformer', and from this it was reasoned that the proper approach to the problem should be-toward effective isolation of the transformer as the sourcey of the ringing currents. An attempt` was made to effect'the desired isolation by the insertion of impedance in theV connection-between the transformer and the yoke, but this proved toi-be unsuctially excluded from the deflection coils.

lCC

transformer, and to the further discovery that the null point could be established `at the optimum location for maximumpower transfer by insertion of 'suitable impedance in series with the transformer during both conduction and non-conduction of the driver tube. Then.'

with ,the deflection yoke connected to the transformer at the ,null` point, the transformer is elfectively isolated from the horizontal 1deflection coils insofar as ringingr currents are concerned, and such currents are substan- This invention effectively provides arlbridge arrangement which maybe balanced, insofar as ringing currents are concerned, topreventl or'minimize delivery of such.

currents to the horizontal deflection-coils.. Balance of the bridge during bothI conduction and non-conduction of the driver tube requires .ditferentvalues of impedance in seri-es With the transformer. In the preferred embodiment of the invention, the different values of impedance are provided by utilizingtwo impedances in parallel repar-allel branches Vso as to of the .impedances The 'invention may be fully understood from the followingdetailed descriptionwith reference to the accompanying drawing, wherein:y

Fig. l isa simplified illustration-of the pertinent por-V lcomprising the output or driver tube 10the output trans- Y formerll which ,is preferably an -autotransformer `as,

shown, the deflecting yoke which includes the horizontal deflecting coilsrepresente-d at 12 associated with the cath- -ode ray tube 13, the damper tube 14, the associated capacitors 15 and 16 and the boosting capacitor 17. These Ielements are connected as shown, the horizontal deflecting coils being connected to the winding of transformer 11 at the 4optimum point 18 for power transfer to the yoke. High voltage isrderived'from the transformer and is rectified for application to the second anode of the cathode ray tube. Disregarding lfor the moment the block labeled-Z, all of the other elements shown are conventionalV and their functions are Well understoodjby those skilled in the art.

`It will be understood that the horizontal deliection -system Ofa television receiver also includes other cornponentsby which a suitable driving voltage is supplied to the control grid of the output or driver tube. Since the present'invention is concerned only with the components shown, there is no need to illustrate or describe other components of the complete system. In Fig. 1, the

components which constitute -a signal source for tube 10" are represented by the labeled block 19.

As hereinbefore mentioned, during operation of the system ringing current tends to be produced in the horizontal deflecting coils, and the present invention is directed toward the elimination or minimization of such current. This inventionfas previously indicated, evolved from the determination that the transformer is a source of transientV ringing voltage', and the discovery that there is a point alongthe transformer, with respect to ground, at which the ringing voltageV goes throughV a null. From this discovery it was deduced that if the-yoke were connectedto the transformer winding at the null point, there Patented Oct. 8, 1957 l would be no ringing currents delivered to the yoke. However, it was found that this point is not usually the optimum point for maximum power transfer or most efficient operation. After considerable experimentation, it was found that the null point could be made to coincide with the optimum point for power transfer by inserting suitable impedance in series between the transformer and ground. In Fig. 1, this inserted impedance is represented by the block Z.

Reference is now made to Fig. 2 for a simplified illustration and explanation of a system embodying the invention. In this illustration, Z is the impedance inserted in accordance with this invention, Z1 is the plate conductance of the output tube, and Z2 is the stray capacitance of the high voltage section. Assume first that Z is omitted or is effectively removed by being short-circuited. If a current were passed through the transformer and then cut off, a current at the ringing frequency would flow through the deflection yoke. Now it has been found that with Z inserted, for a particular value of resistance and reactance of this impedance, the ringing current in the yoke can be reduced substantially to zero. Experimentation has shown that the arrangement illustrated is a bridge circuit which can be balanced at the optimum point 1S for power transfer, insofar as the ringing current is concerned, by means of a suitable impedance Z. If this balance is achieved and maintained throughout the operating cycle, the transformer is effectively isolated from the horizontal deflecting coils, with respect to the ringing voltage in the transformer, and thus no ringing current is delivered to the deflecting coils.

To achieve balance of the circuit throughout the operating cycle, it is necessary that the impedance Z be proper during both conduction and non-conduction of the output or driver tube. When plate current is flowing in this tube, its plate conductance is constant. time, for balance of the circuit it is necessaryv that Z be a relatively low resistance, e. g., approximately 700 to 800 ohms. When the output or driver tube is not conducting, for balance of the circuit it is necessary that Z be a highly resistive and slightly reactive impedance. It is desirable, therefore, to provide suitable means to effect the required changes in the impedance Z during each operating cycle to maintain a balanced condition of the system.

Fig. 3 shows a preferred embodiment of the invention, wherein shunt related impedance elements and a switching diode are employed to provide the required impedance in series with the transformer 11 during both conduction and non-conduction of the driver tube 10. In this embodiment, an adjustable inductor 20 provides a highly resistive and slightly reactive impedance, and a shunt resistor 21 provides a relatively low resistance. A diode 22 is included in the shunt in series with resistor 21, and is poled so as to be conductive only when the plate voltage of the driver tube is positive. With this arrangement, when the plate voltage of tube 10 swings negative following retrace due to energy stored in the transformer, the diode 22 goes out of conduction, rendering high impedance effective to maintain a balance of the circuit as above-described. When the plate voltage of tube 10 goes positive, the diode 22 conducts and this effectively inserts the resistance 21 which balances the plate conductance of tube 1f) and thus maintains a balance of the circuit.

Thus, during non-conduction of the driver tube 10, the impedance element 20 is effective to achieve the desired balance of the circuit, and during conduction of the driver tube 10, the diode 22 conducts and effectively closes the low impedance circuit branch through resistor 21 to compensate for the conductance of the driver tube.

It should be noted that the diode 22 actually serves two purposes. During retrace, the diode provides a low impedance path between the transformer and ground, and therefore Ait improves the efficiency o f the transformer in At this Y supplying high voltage for the cathode ray tube. During the portion of the trace interval when the driver tube 10 is conducting, the diode also conducts to maintain a balance of the circuit.

By way of example only, in one embodiment of the invention in the horizontal deflection circuit of an experimental television receiver, the inductor 20 is adjustable between 5 and l1 mh. and its resistive impedance at ringing frequency is 20,000 to 50,000 ohms. The resistor 21 is adjustable between 500 and 1100 ohms. Capacitors 15, 16 and 17 have values respectively of 20 microfarads, microfarads and 0.5 microfarad.

While a preferred embodiment of the invention has been illustrated and described, it will be understood that the invention is not limited thereto but contemplates such modifications and further embodiments as may occur to those skilled in the art.

I claim:

l. In a horizontal magnetic deflection system for a television receiver wherein an output or driver tube is connected to a transformer, from a winding of which high voltage is derived, and wherein the horizontal deflection coils are connected to an optimum point on said winding for transfer of energy to said coils, the method of preventing or minimizing flow of undesired transient currents in said coils, which comprises introducing impedance in series with said winding effective during nonconduction of said tube to maintain at said point substantially zero value of undesired transient oscillatory voltage produced in said winding as an incident to operation of the system, and introducing impedance in shunt with the first-mentioned impedance during conduction of said tube to compensate for the conductance of said tube and to maintain the aforementioned zero valve at said point.

2. In a horizontal magnetic deflection system for a television receiver having a cathode ray tube, a grid-controlled driver tube to the control grid of which a driving voltage is supplied, an output transformer connected to said driver tube including a winding from which energy for deflection is derived, a deflection yoke for said cathode ray tube having horizontal deflection coils, means connecting said coils to said winding at an optimum point for transfer of energy to the coils, there being an undesired transient oscillatory Voltage produced in said winding as an incident to operation of the system, and means for inserting impedance in series with said winding at the low potential end thereof effective to establish and maintain substantially zero value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current flow to said coils.

3. In a horizontal magnetic deflection system for a television receiver having a cathode ray tube, a gridcontrolled driver tube to the control grid of which a driving voltage is applied, an output transformer connected to said driver tube including a winding from which energy for deflection is derived and from which high voltage for said cathode ray tube is also derived, a deflection yoke for said cathode ray tube having horizontal deflection coils, means connecting said coils to said winding at an optimum point for transfer of energy to the coils, there being an undesired transient oscillatory voltage produced in said winding as an incident to operation of the system, and means for inserting impedance of one value in series with said winding during conduction of said driver tube, and for inserting impedance of a different value in series with said winding during non-conduction of said driver tube, the impedance values being effective to establish and maintain substantially zero Value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current flow to said coils.

.4. In a horizontal magnetic deflection system for a television receiver having a cathode ray tube, a gridcontrolled driver tube to the control grid of which a driving voltage is supplied, an output transformer connected to said driver tube including a Winding from which energy for dellection is derived and from which high voltage for said cathode ray tube is also derived, a deflection yoke for said cathode ray tube having horizontal deilection coils, means connecting said coils to said Winding atan optimum point for transfer of energy to the coils, there being an undesired transient oscillatory voltage produced in said winding as an incident to operation of the system, a high impedance connected to the low potential end of said winding in series therewith, a relatively low impedance in shunt with said high impedance, and means for closing and opening the shunt during conduction and non-conduction respectively of said driver tube, said impedances being elfective to maintain substantially zero value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current llow to said coils.

5. A system according to claim 4, wherein said high impedance is an nductor, said low impedance is a resistor, and said means for closing and opening the shunt through the latter is a diode.

6. In a horizontal magnetic deflection system for a television receiver having a cathode ray tube, a gridcontrolled driver tube to the control grid of which a driving voltage is supplied, an output autotransformer connected to said driver tube for transfer of energy for deflection and also serving to provide high voltage for said cathode ray tube, a boosting capacitor connected to one end of said transformer, a deflection yoke for said cathoderay tube having horizontal deflection coils, means connecting said coils to said transformer at an optimum point for transfer of energy to the coils, there being an undesired transient oscillatory voltage produced in said transformer as an incident to operation of the system, and means for inserting serially between said transformer and said capacitor impedance effective to establish and maintain substantially zero value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current ow in said coils.

7. In a horizontal magneticdeflection system for a television receiver having a cathode ray tube, a gridcontrolled driver tube to the control grid of which a driving voltage is supplied, an output autotransformer connected to said driver tube for transfer of energy for deflection and also serving to provide high voltage for said Cathode ray tube, a boosting capacitor connected to one end of said transformer, a deflection yoke for said cathode ray tube having horizontal deflection coils, means connecting said coils to said transformer at an optimum point for transfer of energy to the coils, there being an undesired transient oscillatory voltage produced in said transformer as an incident to operation of the system, and means for inserting impedance of one value serially between said transformer and said capacitor during conduction of said driver tube, and for inserting impedance of a different value serially between said transformer and said capacitor during non-conduction of said driver tube, the impedance values being elfective to establish and maintain substantially zero value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current flow in said coils.

8. In a horizontal magnetic deflection system for a television receiver having a cathode ray tube, a gridcontrolled driver tube to the control grid of Which a driving voltage is supplied, an output autotransformer connected to said driver tube for transfer of energy for deflection and also serving to provide high voltage for said cathode ray tube, a boosting capacitor connected to one end of said transformer, a deflection yoke for said cathode ray tube having horizontal deflection coils, means connecting said coils to said transformer at an optimum point for transfer of energy to the coils, there being an undesired transient oscillatory voltage produced in said transformer as an incident to operation of the system, a high impedance serially connected between said transformer and said capacitor, a relatively low impedance in shunt with said high impedance, and means for closing and opening the shunt during conduction and non-conduction respectively of said driver tube, said impedances being effective to maintain substantially zero value of said oscillatory voltage at said point, thereby effectively to isolate said transformer from said coils with respect to said oscillatory voltage and thus prevent undesired current ow in said coils.

9. A system according to claim 8, wherein said high impedance is an nductor, said low impedance is a resistor, and said means forrclosing and opening the shunt through the latter is a diode.

References Cited in the ille of this patent UNITED STATES PATENTS 2,555,831 Tourshou a June 5, 1951 2,613,334 Otis et al Oct. 7, 1952 2,686,276 Anderson Aug. 10, 1954 2,742,591 Procter Apr. 17, 1956 '2,743,381 Dietch Apr. 24, 1956 

